Endpoint detector and method for measuring a change in wafer thickness in chemical-mechanical polishing of semiconductor wafers

Abstract

The present invention is an endpoint detector and a method for quickly and accurately measuring the change in thickness of a wafer in chemical-mechanical polishing processes. The endpoint detector has a reference platform, a measuring face, and a distance measuring device. The reference platform is positioned proximate to the wafer carrier, and the reference platform and measuring device are positioned apart from one another by a known, constant distance. The measuring face is fixedly positioned with respect to the wafer carrier at a location that allows the measuring device to engage the measuring face when the wafer is positioned on the reference platform. Each time the measuring device engages the measuring surface, it measures the displacement of the measuring face with respect to the measuring device. The displacement of the measuring face is proportional to the change in thickness of the wafer between measurements.

What is claimed is:  
     
       1. In planarization of wafers, a method for measuring a change in thickness of a wafer attached to a wafer carrier of a planarizing machine, the method comprising: 
       measuring a first relative elevation of a surface of the wafer carrier with respect to a reference platform; and  
       re-measuring a second relative elevation of the surface of the wafer carrier with respect to the reference platform after planarizing the wafer for a period of time, a difference between the first and second elevations being indicative of the change in wafer thickness.  
     
     
       2. The method of claim  1  wherein measuring the first elevation comprises: 
       pressing the wafer against the reference platform; and  
       engaging the surface of wafer carrier with a measuring device that determines the first relative elevation of the surface of the wafer carrier with respect to the reference platform.  
     
     
       3. The method of claim  2  wherein re-measuring the second elevation comprises: 
       planarizing the wafer after engaging the surface of the wafer carrier with the measuring device to determine the first elevation of the wafer carrier;  
       pressing the wafer against the reference platform subsequent to planarizing the wafer; and  
       re-engaging the surface of the wafer carrier with the measuring device to determine the second relative elevation of the surface of the wafer carrier with respect to the measuring platform.  
     
     
       4. The method of claim  3  wherein the reference platform comprises a body separate from a polishing pad of the planarizing machine, and wherein: 
       pressing the wafer against the reference platform for measuring the first relative elevation of the wafer carrier comprises moving the wafer over the reference platform and placing the wafer on the platform; and  
       pressing the wafer against the reference platform for re-measuring the second elevation of the wafer carrier comprises removing the wafer from the polishing pad, positioning the wafer over the reference platform, and re-placing the wafer on the platform.  
     
     
       5. The method of claim  4  wherein engaging and re-engaging the surface of the wafer carrier with the measuring device comprises impinging a light beam of an interferometer onto a measuring face defined by a top surface of the wafer carrier. 
     
     
       6. The method of claim  4  wherein engaging and re-engaging the surface of the wafer carrier with the measuring device comprises impinging a light beam of an interferometer onto a measuring face defined by a planar, reflective panel attached to a top surface of the wafer carrier. 
     
     
       7. The method of claim  3  wherein the reference platform comprises a polishing pad of the planarizing machine, and wherein: 
       pressing the wafer against the reference platform for measuring the first relative elevation of the wafer carrier comprises contacting the wafer with a planarizing surface of the polishing pad; and  
       pressing the wafer against the reference platform for re-measuring the second relative elevation of the wafer carrier comprises maintaining contact between the wafer and the planarizing surface of the polishing pad.  
     
     
       8. The method of claim  7  wherein engaging and re-engaging the surface of the wafer carrier with the measuring device comprises impinging a light beam of an interferometer onto a measuring face defined by a top surface of the wafer carrier. 
     
     
       9. The method of claim  7  wherein engaging and re-engaging the surface of the wafer carrier with the measuring device comprises impinging a light beam of an interferometer onto a measuring face defined by a planar, reflective panel attached to a top surface of the wafer carrier. 
     
     
       10. The method of claim  3  wherein the reference platform comprises a body attached to a platen of the planarizing machine other than a polishing pad, and wherein: 
       pressing the wafer against the reference platform for measuring the first relative elevation of the wafer carrier comprises moving the wafer over the reference platform and placing the wafer on the platform; and  
       pressing the wafer against the reference platform for re-measuring the second relative elevation of the wafer carrier comprises removing the wafer from the polishing pad, positioning the wafer over the reference platform, and re-placing the wafer on the platform.  
     
     
       11. The method of claim  10  wherein engaging and re-engaging the surface of the wafer carrier with the measuring device comprises impinging a light beam of an interferometer onto a measuring face defined by a top surface of the wafer carrier. 
     
     
       12. The method of claim  10  wherein engaging and re-engaging the surface of the wafer carrier with the measuring device comprises impinging a light beam of an interferometer onto a measuring face defined by a planar, reflective panel attached to a top surface of the wafer carrier. 
     
     
       13. The method of claim  10  wherein the polishing pad has a hole and the body is positioned in the hole, and wherein placing the wafer on the reference platform comprises moving the wafer across a planarizing surface of the polishing pad and onto the body. 
     
     
       14. The method of claim  10  wherein the polishing pad has a hole and the body is defined by a top surface of the platen exposed in the hole, and wherein placing the wafer on the reference platform comprises inserting the wafer into the hole and contacting the wafer with the top surface of the platform.